How to Use the Measure App on an iPhone

Open the Measure app on your iPhone. The Measure app has a very dark background (almost black) but has a set of gradients on the top and bottom with a yellow dotted line connecting two points in between, and marked by "Measure" below it.

Move your phone around the area. The iPhone is looking for flat surfaces to measure items. When it's ready to start diagnosing, it'll say "Move iPhone to start" and won't diagnose the measurements until you perform this needed step for as long as the phone wants you to wave it around. It may say "Continue to move iPhone" if you aren't moving the phone fast enough, or too fast.

Look for the screen to show a black dot with a circular ring around it. If the phone can't find a valid starting point in the view, it'll say "Find a nearby surface to measure" or "Move closer." On some flat surfaces (such as tables), if you lay a square item down, the phone will recognize that there's an item it can measurement without much input and with a single tap, allow you to open the item for a measurement.

Tap the plus sign button at the bottom of the screen when the crosshair icon appears. This begins the measurement.

Move your phone to the final location where you'd like the measurement to stop. You can't stop in mid-space, but you can extend the line past the edges of walls into other flooring areas connecting the area. "Drag" your phone to mark the best path for the measurement. A yellow-dashed line will result.

Tap the plus button again at the bottom when you are done marking the location.

Read the measurement. As you mark the endpoint of the line, you'll see the measurement approximation by a yellow-filled oval at the mid-area of the segment. Once you mark the endpoint, if you just need the imperial units, it'll read its measurement in half inch increments - but if you tap the black button, it'll give you the metric approximation without mentioning its units (centimeters). If you'd like to transmit this information to someone else, opening up the button for the two measurements will produce a "Copy" button that you can use to copy the details to the clipboard and paste to other locations.

Recognize how measurements get cleared. There's a one-touch "Clear" button at the top right corner of the screen that - when tapped, clears all measurements at the same time.